Wireless communications system, base station, and mobile station

ABSTRACT

A wireless communications system including a mobile station MS and base stations BS 1  and BS 2 , wherein one or both of the mobile station MS and the base stations BS 1  and BS 2  is provided with a unit for notifying information of a frame position with the possibility of transmission of packets based on detection of deterioration of a reception quality and wherein the mobile station MS is provided with a unit for determining a frame position without the possibility of transmission of packets and shifting to a peripheral cell detection mode at this frame position based on information of a frame position with the possibility of transmission of packets, whereby it is possible to shift to a peripheral cell detection mode without lowering the transmission efficiency and without complicating the processing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communications system, abase station, and a mobile station, wherein the mobile station performswireless communication with the base station with handover beingsmoothly executed.

2. Description of the Related Art

At the present time, a variety of wireless communications systems arebeing put into practical use. One such wireless communications system isthe W-CDMA (Wideband-Code Division Multiple Access) system. Further, theHSDPA (High Speed Downlink Packet Access) using W-CDMA to raise thetransmission rate in the downlink by a maximum of 14 Mbps. An adaptivemodulation and coding scheme is used in HSDPA systems wherein the systemadaptively switches, for example, between a QPSK (Quadrature Phase ShiftKeying) modulation scheme and a 16-value QAM (Quadrature AmplitudeModulation) scheme so as to obtain the transmission rate correspondingto the state of the wireless transmission line.

In the HSDPA system, an H-ARQ (Hybrid Automatic Repeat Request) mode isemployed. When a mobile station detects an error in reception data froma base station, it requests retransmission of data from the basestation. Then the base station retransmits the data and the mobilestation performs error correction and decoding processing using both thepreviously received data and the retransmitted data (refer to, forexample, 3GPP TS 25.211 v5.5.0 (3rd Generation Partnership Project;Technical Specification Group Radio Access Network; Physical channelsand mapping of transport channels onto physical channels (FDD)) or 3GPPTS 25.212 v5.9.0 (3rd Generation Partnership Project; TechnicalSpecification Group Radio Access Network; Multiplexing and channelcoding (FDD)).

Further, the main wireless channels in the HSDPA system include anHS-SCCH (High Speed-Shared Control Channel), HS-PDSCH (HighSpeed-Physical Downlink Shared Channel), HS-DPCCH (High-Speed-DedicatedPhysical Control Channel), etc.

The HS-SCCH and HS-PDSCH channels explained above are shared channels ofthe down side (downlink) from a base station to a mobile station in awireless communications system, and the HS-SCCH is a control channel fortransmitting a variety of parameters concerning data transmitted by theHS-PDSCH and a channel for pre-announcement of data transmission. Suchparameters include, for example, modulation type information indicatingthe modulation scheme for transmitting the data by the HS-PDSCH, thenumber of spreading codes, and the pattern information of rate matchingprocessing applied to the transmission data.

Further, the HS-DPCCH is an individual control channel at the up side(uplink) from a mobile station to a base station in a wirelesscommunications system and is used when transmitting an ACK signal or aNACK signal corresponding to whether normal reception of the datareceived by the HS-PDSCH is possible or not from the mobile station tothe base station. For example, in a case a CRC error is detected in thereception data, etc., the mobile station transmits a NACK signal to thebase station. The base station will then perform processing forretransmission based on the NACK signal. Further, the HS-DPCCH is usedto report the reception quality (for example SIR (Signal to InterferenceRatio)) of the received signal from the base station and periodicallytransmits the result as a CQI (Channel Quality Indicator) to the basestation. The base station judges the quality of the wireless environmentin the downlink based on this CQI, switches the modulation scheme to themodulation scheme making higher speed transmission of data possible whenthe wireless environment is good, or, conversely, switches themodulation scheme to the modulation scheme for transmitting the data ata lower speed when the wireless environment is poor.

FIG. 9 is an explanatory view of the channels in the HSDPA and showsschematic views of a CPICH, P-CCPCH, HS-SCCH, HS-PDSCH, and HS-DPCCH.The CPICH (Common Pilot Channel) and P-CCPCH (Primary Common ControlPhysical Channel) are common channels in the downlink, wherein the CPICHis a channel utilized for channel estimation, a cell search, and as atiming standard of the other downlink physical channels in the same cellin the mobile station and as a channel for transmitting a so-calledpilot signal. Further, the P-CCPCH is a channel for transmittingbroadcast information. Further, HS-SCCH, HS-PDSCH, and HS-DPCCH show theabove wireless channels and transmit the above CQI and ACK/NACK byHS-DPCCH.

Further, since 15 slots comprise 1 frame, and CPICH is used as thetiming standard, the frame heads of P-CCPCH and HS-SCCH coincide withthe frame head of the CPICH, but the frame head of HS-PDSCH is delayedby the amount of 2 slots. This allows the mobile station to receiveinformation required to demodulate and discriminate the HS-PDSCH aheadof time. Hence, this information is used in the demodulation anddecoding of the HS-PDSCH by notifying, in advance, information regardingthe modulation scheme, spreading codes, etc., for pre-announcement bythe HS-SCCH. Further, in the HS-SCCH and HS-PDSCH, 3 slots comprise 1sub frame.

Referring to 3GPP, TS25.212v.5.7.0, the information by the HS-SCCH isdescribed below in (a) to (g).

(a) Xccs (Channelization Code Set Information); 7 bits; Information ofspreading codes used in HS-DSCH.

(b) Xms (Modulation Scheme Information); 1 bit; Modulation scheme usedin HS-DSCH.

(c) Xtbs (Transport-Block Size Information); 6 bits; Block size of errorcorrected and encoded transmission data.

(d) Xhap (Hybrid-ARQ Process Information); 3 bits; Retransmissioncontrolled process number.

(e) Xrv (Redundancy and Constellation Version); 3 bits; Parameter ofrate matching.

(f) Xnd (New Data Indicator); 1 bit; Information of whether is it newdata.

(g) Xue (UE Identity); 16 bits; User identification information.

As described above, the HS-SCCH has a structure of 37 bits in total. Byreceiving the HS-SCCH, parameters used in the HS-DSCH, such as, themodulation scheme, spreading codes, and error correction can be learned.Accordingly, the HS-PDSCH can be demodulated and decoded according tothese parameters.

Xccs described above in (a) indicates the spreading codes when the datais transmitted by the HS-PDSCH and can indicate, for example, acombination of the number of multi-codes and code offset. Further, Xmsdescribed above in (b) indicates whether the modulation scheme is, forexample, QPSK or 16 QAM by a “0” or “1”. Further, Xtbs described abovein (c) indicates data for calculating the size of data transmitted by 1sub frame of the HS-PDSCH, and Xhap described above in (d) indicates theprocess number of H-ARQ and uses the same number as the process numberof the transmission data of the previous time at the time ofretransmission.

Further, Xrv described above in (e) indicates the redundancy versionparameter and the constellation parameter at the time of retransmissionof the HS-PDSCH and includes a case where the parameters are updated anda case where the parameters are not changed in new transmission andretransmission. Further, Xnd described above in (f) is data indicatingwhether the transmission block of the HS-PDSCH is a new block or aretransmission block. A new block alternately changes the data between“1” and “0”, while a retransmission block keeps the data the same asbefore, i.e., does not change the data. This enables the two to bedifferentiated. Further, Xue described above in (g) is identification(ID) information of the mobile station (user).

By receiving the HS-SCCH, the parameters of the modulation scheme,spreading codes, and error correction applied in the HS-PDSCH arerecognized, and demodulation and decoding of the HS-PDSCH can be carriedout (refer to 3GPP TS 25.211 v5.5.0, 3GPP TS 25.212 v5.9.0, 3GPP TS25.214 v5.7.0 (3rd Generation Partnership Project; TechnicalSpecification Group Radio Access Network; Physical layer procedures(FDD)).

A simple explanation will be given of the operation of packettransmission applying the HSDPA system to the above W-CDMA system.

The base station transmits the data via the shared channel (HS-PDSCH)and selects the mobile station to which data is to be transmitted viathis shared channel from among a plurality of mobile stations. Then, thebase station sequentially transmits the radio frames storing the dataaddressed to the selected mobile station. At this time, the base stationpre-announces the transmission of data prior to data transmission viathe control channel (HS-SCCH).

For example, as shown in FIG. 10, the base station transmits signalingby the control channel (HS-SCCH) indicating transmission of data(packets) when transmitting data (packets) to a certain mobile station.On the other hand, the mobile station constantly monitors this controlchannel and performs processing for reception of the data packets bydetecting signaling addressed to it.

It should be noted that, in FIG. 10, the signaling signals, indicated bybroken lines, indicate signals addressed to other mobile stations, thecase where the mobile station for the pre-announcement of transmissiondoes not exist, or the case where a signaling signal is not to betransmitted. Naturally data for a portion in which the signaling signalis not transmitted is not transmitted.

As explained above, when transmitting data from the base station via theshared channel and performing handover processing, the mobile stationmust measure the received signal from a peripheral cell. For such ahandover, the following technique has been proposed.

For example, in a wireless communications system asynchronouslyperforming packet communication, the mobile station receives a beacontransmitted from a base station at a constant cycle, measures the levelof reception and, when the measurement result is less than a thresholdvalue, transmits a state transition packet to the base station andshifts to a communication suppression mode such as a power save mode. Awireless communications system has been proposed in which the mobilestation stops transmitting and receiving data in this communicationsuppression mode, searches for another base station during thiscommunication suppression mode and, when shifting from thiscommunication suppression mode to the normal mode, transmits a statetransition packet and returns to the normal mode (refer to, for example,Japanese Unexamined Patent Publication (Kokai) No. 2003-158481).

Further, in a wireless communications system using the TDMA system, awireless communications system has been proposed which detects the fieldstrength of a transmission signal from a peripheral cell by utilizingthe time of idle time slots originally not used by the mobile stationand transmits the detection result to a base station to request handover(refer to, for example, Japanese Unexamined Patent Publication (Kokai)No. 3-268697).

In order for a mobile station to secure handover in a wirelesscommunications system, it therefore has to detect a peripheral cell, butprovisioning a receiving unit merely for the detection of a peripheralcell is impractical/impossible, both in terms of space and in terms ofpower consumption. Accordingly, the mobile station detects a peripheralcell using the frequency of the peripheral cell, the wireless accessscheme, etc. However, in the HSDPA and next generation mobilecommunications, signals are transmitted and received by the packetformat through a shared channel. Therefore, there are cases wheresignals are transmitted in frames of consecutive packets and cases wheresignals are intermittently transmitted. Whether or not such packets aretransmitted is notified for each frame by the signaling from the basestation. Therefore, a mobile station must constantly receive the signalfrom the base station. This makes it difficult to detect the peripheralcell efficiently.

Further, in the conventional example where a mobile station receives abeacon and shifts to a communication suppression mode when the result ofmeasurement of the level of reception is less than a threshold value,there is a problem in that a period where no data can be received at allis continuously generated for a predetermined time during thiscommunication suppression mode.

Namely, this presents a problem in that the transmission efficiency isremarkably lowered. Further, in order to store data in thiscommunication suppression mode, it is necessary to provide a buffermemory having a relatively large storage capacity.

SUMMARY OF THE INVENTION

An object of the present invention is to suppress the deterioration oftransmission efficiency when detecting a peripheral cell for handover ina case where data is transmitted via a shared channel.

To attain the above object, according to the present invention, there isprovided a wireless communications system for packet communicationsbetween a mobile station and a base station, wherein at least one mobilestation and base station notifies a frame position with the possibilityof transmission of packets and the mobile station shifts to a peripheralcell detection mode at a frame position without the possibility oftransmission of packets other than a frame position with the possibilityof transmission of packets.

Further, the present invention teaches the notification of a frameposition with the possibility of transmission of packets by one signalbetween the mobile station and the base station.

Further, according to the present invention, the mobile stationdetermines that a next frame position is also a frame position with thepossibility of transmission of packets when packet transmission isactually carried out at a frame position with the possibility oftransmission of packets determined between the mobile station and thebase station, and determines that a next frame position is a frameposition without the possibility of transmission of packets when frametransmission is actually not carried out at a frame position with thepossibility of transmission of packets, and shifting to a peripheralcell detection mode at a frame position without the possibility oftransmission of packets.

Further, at least one mobile station and base station notifies a frameposition with the possibility of transmission of packets based on aframe period and an offset value of the packet transmission, making atleast one of the frame period and the offset value different for atleast one of the mobile station and the base station, and notifying thisbetween the mobile station and the base station.

Further, the base station of the present invention is a base station forpacket communications with a mobile station and is provided with anotifying unit for notifying a frame position with the possibility oftransmission of packets to the mobile station and a controlling unit foractivating the notifying unit when detecting that a reception qualityaccording to reception quality information from the mobile station fallsto less than a threshold value.

Further, the notifying unit (for notifying the frame position with thepossibility of transmission of packets) is designed to make at least oneof the period (indicating frame positions with the possibility oftransmission of packets and the offset value) different for a cell orsector and notifying unit notifies the same to the mobile station.

Further, provision is made for making at least one of the period(indicating frame positions with the possibility of transmission ofpackets) and the offset value different for the mobile station and fornotifying the same.

Further, the mobile station of the present invention is a mobile stationfor packet communications with a base station, wherein the mobilestation receives a signal from the base station, detects a receptionquality of the received signal, and transmits a request for shifting toa peripheral cell detection mode to the base station when the receptionquality falls to less than a threshold value and determines a frameposition without the possibility of transmission of packets from a frameposition with the possibility of transmission of packets notified withthe base station and shifts to the peripheral cell detection mode at aframe position without the possibility of transmission of packets.

The mobile station is provided with a measuring unit for receiving asignal from a base station and measuring the quality of the receivedsignal, a transmitting unit for transmitting information of thereception quality measured by the measuring unit to the base station, acomparing unit for comparing the reception quality against a thresholdvalue, a transmitting unit for transmitting a request for shifting to aperipheral cell detection mode to the base station when detecting thatthe reception quality falls to less than the threshold value (using thecomparing unit), and a discriminating unit for discriminating a frameposition without the possibility of transmission of packets according tothe information of a frame position with the possibility of transmissionof packets based on the period and offset value notified with the basestation and shifting to the peripheral cell detection mode at a frameposition without the possibility of transmission of packets.

Further, the mobile station is further provided with a determining unitfor determining if a next frame position is also a frame position withthe possibility of transmission of packets when packet transmission isactually carried out at the frame position with the possibility oftransmission of packets notified to the base station, determining that anext frame position is a frame position without the possibility oftransmission of packets when the packet transmission is actually notcarried out at the frame position with the possibility of transmissionof packets, and shifting to the peripheral cell detection mode at theframe position without the possibility of transmission of packets.

Further, according to another aspect of the present invention, there isprovided a wireless base station able to sequentially transmit wirelessframes storing data addressed to a mobile station selected from among aplurality of mobile stations wherein the wireless base station isprovided with a detecting unit for detecting a specific mobile stationrequiring measurement of a received signal from a peripheral cell and acontrolling unit for discontinuously generating wireless frames notstoring data for the specific mobile station among the wireless framessequentially transmitted after detection by the detecting unit andincluding the specific mobile station in the candidates for theselection for wireless frames between discontinuously generated adjacentwireless frames.

Further, the discontinuously generated wireless frames store dataaddressed to other mobile stations.

Further, according to another aspect of the present invention, there isprovided a wireless base station able to sequentially transmit wirelessframes storing data addressed to a mobile station selected from among aplurality of mobile stations, wherein the wireless base station isprovided with a detecting unit for detecting a specific mobile stationrequiring measurement of a received signal from a peripheral cell, anotifying unit for notifying information enabling identification ofdiscontinuous wireless frames not storing data for the specific mobilestation to the specific mobile station, and a controlling unit forgenerating discontinuous wireless frames not storing data for thespecific mobile station (after notification by the notifying unit) andincluding the specific mobile station in the candidates for selectionfor wireless frames between the discontinuously generated adjacentwireless frames.

Further, the information enabling identification may be informationenabling identification of discontinuous wireless frames based onpre-announcement of transmission of wireless frames storing dataaddressed to the specific mobile station or information enablingidentification of discontinuous wireless frames based on wireless framesstoring data addressed to the specific mobile station.

Further, according to another aspect of the present invention, there isprovided a mobile station for receiving a wireless signal from awireless base station able to sequentially transmit wireless framesstoring data addressed to the mobile station selected from among aplurality of mobile stations, wherein the mobile station is providedwith an evaluating unit for receiving a wireless signal from a wirelessbase station different from the wireless base station during a period ofdiscontinuous wireless frames not storing data for itself generated bythe wireless base station and evaluating the same when it requiresmeasurement of a received signal from a peripheral cell. Further, themobile station can be configured so that information enablingidentification of discontinuous wireless frames is notified from thewireless base station.

By the above configurations, the present invention achieves at least thefollowing advantages.

When a mobile station detects a peripheral cell for handover, a drop inthe transmission efficiency is suppressed. Further, a flexible wirelesscommunications system can be constructed by making the period betweenframe positions with the possibility of transmission of packets andoffset value different for the mobile station or for the sector and lossof transmission packets can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and features of the present invention will be moreapparent from the following description of the preferred embodimentsgiven with reference to the accompanying drawings, wherein:

FIGS. 1A and 1B are explanatory views of a first embodiment of thepresent invention;

FIGS. 2A and 2B are explanatory views of principal parts of transmissionand reception functions of a base station;

FIGS. 3A and 3B are explanatory views of principal parts of transmissionand reception functions of a mobile station;

FIGS. 4A and 4B are explanatory views of a second embodiment of thepresent invention;

FIGS. 5A and 5B are explanatory views of a third embodiment and fourthembodiment of the present invention;

FIG. 6 is an explanatory view of a fifth embodiment of the presentinvention;

FIGS. 7A and 7B are explanatory views of a sixth embodiment of thepresent invention;

FIGS. 8A and 8B are explanatory views of a seventh embodiment and eighthembodiment of the present invention;

FIG. 9 is an explanatory view of a channel configuration in the HSDPA;and

FIG. 10 is an explanatory view of packet transmission using aconventional shared channel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail below while referring to the attached figures.

Referring to FIGS. 1A and 1B, the wireless communications system of thepresent invention is a wireless communications system for packetcommunications between a mobile station MS and a base station BS1,wherein one or both the mobile station MS and base station BS1 is ableto notify a frame position with the possibility of transmission ofpackets, and the mobile station MS is able to shift to a peripheral celldetection mode at a frame position without the possibility oftransmission of packets other than a frame position with the possibilityof transmission of packets and able to smoothly achieve handover.

Further, the base station of the present invention is a base station BS1for packet communications with a mobile station MS, wherein the basestation BS1 notifies a frame position with the possibility oftransmission of packets to the mobile station MS and activates suchnotification when it detects that a reception quality, according toreception quality information (CQI: Channel Quality Information), fromthe mobile station MS falls to less than a threshold value.

Further, the mobile station of the present invention is a mobile stationMS for packet communications with a base station BS1, wherein the mobilestation MS receives a signal from the base station BS1, detecting thereception quality thereof, and transmits a request to shift to aperipheral cell detection mode to the base station BS1 when thereception quality falls to less than a threshold value and determines aframe position without the possibility of transmission of packets from aframe position with the possibility of transmission of packets notifiedwith the base station BS1 and shifts to the peripheral cell detectionmode at a frame position without the possibility of transmission ofpackets.

Further, the wireless base station BS1 sequentially transmits wirelessframes storing data addressed to a mobile station selected from among aplurality of mobile stations via a shared channel (for example,HS-PDSCH) and detects a specific mobile station MS requiring measurementof a received signal from a peripheral cell (for example, a pilot signal(CPICH) transmitted from the peripheral cell) (detects this by; forexample, receiving a report of deterioration of the reception qualityfrom a mobile station MS or receiving a peripheral cell detectionrequest from a mobile station detecting deterioration of the receptionquality). After the detection, the wireless base station BS1 generatesdiscontinuous wireless frames (sub frames of HS-PDSCH) not storing datafor this specific mobile station MS. Then, it includes this specificmobile station MS in the candidates for selection of the mobile stationfor transmission of data via the shared channel for the wireless framesbetween these discontinuously generated wireless frames. Based on such asetup, the specific mobile station can receive data between thediscontinuous wireless frames. Naturally, the discontinuous wirelessframes not storing data for the specific mobile station MS can storedata addressed to other mobile stations. Also, for the specific mobilestation, it is not necessary to include a frame for which storage of thedata is completely prohibited in the shared channel (for exampleHS-PDSCH). Preferably, the wireless base station BS1 notifiesinformation enabling identification of discontinuous wireless frames notstoring data to this specific mobile station MS1. By this, even if notpreviously determined, it becomes possible to identify the discontinuousframes.

It should noted that the identification of the discontinuous framesincludes a case where discontinuous frames are identified with referenceto data transmitted addressed to this specific mobile station MS and acase where discontinuous frames are specified with reference topre-announcement of transmission of data to be transmitted addressed tothis specific mobile station MS. Further, the corresponding mobilestation receives a wireless signal (for example a pilot signal (CPICH))from another wireless base station BS2 and evaluates it by utilizing theperiod of transmission of discontinuous wireless frames generated by thewireless base station. The evaluation includes the detection of aperipheral cell (measurement of reception quality such as receptionlevel and reception SIR) for the handover. It should be noted that it isalso possible to detect discontinuous wireless frames by receivinginformation identifying discontinuous wireless frames from the wirelessbase station.

First Embodiment

FIGS. 1A and 1B are explanatory views of a first embodiment of thepresent invention, in which FIG. 1A shows an outline of the wirelesscommunications system and shows a case of a wireless communicationssystem where a base station BS1 transmits data at a frequency f1 and abase station BS2 transmits data by a frequency f2 (frequency differentfrom f1). It should be noted that as an example, the present inventionis described in conjunction with the previously explained WCDMA mobilecommunications system, but, other systems, such as, mobilecommunications systems employing HSPDA and next generation mobilecommunications systems can also be used in conjunction the presentinvention without departing from the scope of the present invention.

The mobile station MS wirelessly communicates with the base station BS1(during service for reception of data via a shared channel as in theHSDPA). When moving to the direction of the base station BS2 whilereceiving packets, the reception quality (for example, reception powerof the pilot signal) from the base station BS1 gradually falls.Therefore, the processing for detection of a peripheral cell becomesnecessary in order to perform handover. In this case, the base stationBS2 of the peripheral cell transmits data at the frequency f2. Themobile station MS cannot simultaneously receive the frequencies f1 andf2, therefore switches the reception frequency to the frequency f2 andshifts to the mode for detection of a peripheral cell by the commonchannel reception. In that case, the base station is able to determine aframe position with the possibility of transmission of packets (forexample, transmission of data in units of frames having predeterminedlengths via the shared channel as in the HS-PDSCH) and a frame positionwithout that possibility (and notifying the same via the controlchannel), while the mobile station MS is able to shift to a peripheralcell detection mode at a frame position without the possibility oftransmission of packets, thereby shifting to the peripheral celldetection mode.

FIG. 1B shows frame positions with the possibility of transmission ofpackets by hatching. The other portions show examples of frame positionswithout the possibility of transmission of packets. Without shifting tothe compressed mode explained above, the mobile station MS shifts to theperipheral cell detection mode at a frame position without thepossibility of transmission of packets (period of transmission ofdiscontinuous frames) determined with the base station BS1. In thisperipheral cell detection mode, the mobile station MS switches thefrequency from f1 to f2 and measures the reception quality from the basestation BS2. Namely, the mobile station MS has a measuring unit formeasuring the reception quality of the signal by the frequency f1 fromthe base station BS1. It compares the information of this receptionquality and the threshold value. When detecting that the receptionquality falls to less than the threshold value, the mobile station MStransmits a request for shifting to the peripheral cell detection modeto the base station BS1. Alternatively, the mobile station MS transmitsthe information of the reception quality to the base station BS1, andthe base station BS1 instructs the mobile station MS to shift to theperipheral cell detection mode when the reception quality falls to lessthan the threshold value in the base station BS1. Then, the base stationBS1 notifies the information of a frame position with the possibility oftransmission of packets between the base station BS1 and the mobilestation MS, and the mobile station MS decides the position is a frameposition without the possibility of transmission of packets and shiftsto the peripheral cell detection mode. Namely, the mobile station MSswitches the frequency to f2 and receives the signal of the commonchannel from the base station BS2.

For example, by limiting the numbers of the frames with the possibilityof transmission of packets to frames designated by a period A and anoffset value B such as A×n+B (where n is an integer), it is possible touse the period of frames without the possibility of transmission ofpackets and switch the frequency or the receiving scheme to detect acell having a different frequency or a cell of a different system in aperipheral cell detection mode. The period A and the offset value B canbe made variable in accordance with the type of the data of thecommunications in the visiting cell (the permitted delay time and bitrate to be guaranteed for are different), the user ID, the ability ofthe user equipment, etc. Further, it is also possible to transmit thepackets by consecutive frames. Further, the numbers of frames with thepossibility of transmission of packets of the head of continuous packetscan be determined as A×n+B (where n is an integer), as explained above.

It is also possible to have the base station BS notify a specific mobilestation that it will not pre-announce transmission (will not transmitpackets) to this specific mobile station (the mobile station requiringdetection of a peripheral cell) after 1 frame and 3 frames afterpre-announcement of transmission and have this specific mobile stationdetect a peripheral cell after 1 frame and 3 frames from the receptionof the pre-announcement of transmission addressed to itself and receivea signal through the channel performing the pre-announcement oftransmission after the 2 frames in the term of the discontinuous framesfrom after 1 frame to after 3 frames. By performing this, the mobilestation MS can detect a peripheral cell in the period of transmission ofdiscontinuous frames for example after 1 frame and after 3 frames. Atthe same time, the possibility of transmission performed to itselfremains for the 2 frames. The occurrence of a continuous period where astation cannot be transmitted to at all can therefore be prevented.

It should be noted that, it is also possible not to use thepre-announcement of transmission as a standard and not to pre-announcetransmission to a specific mobile station (a mobile station requiringdetection of a peripheral cell) for a period after 1 frame and after 3frames from the packet transmission. It is also possible for the mobilestation and the base station to store a particular rule of discontinuouswireless frames not to be transmitted and identify discontinuouswireless frames based on the stored particular rule. For example, bystoring a rule not to transmit for a period after 2 frames and after 5frames with reference to a frame transmitting (receiving) a request ofdetection of a peripheral cell, they can mutually match with each other.

Further, the case of starting a shift to the peripheral cell detectionmode includes, for example, a case of comparing the value of CQI(Channel Quality Information) reported to the base station BS1 and thethreshold value detecting that the CQI has fallen to less than athreshold value. At this time, the shift can be performed autonomouslyby the decision of the mobile station MS (note a report is made to thebase station). At that time, the system can be configured so thatrequested values of the period A and offset value B are transmitted tothe base station BS1 or so that the values of the period A and theoffset value B are designated from the base station BS1. Further, thesystem can be configured so that when the value of the CQI reported fromthe mobile station MS becomes less than the threshold value, a shift tothe peripheral cell detection mode is instructed to the mobile stationMS by the decision of the base station BS1. At that time, the values ofthe period A and the offset value B are designated from the base stationBS1. It is also possible to transmit the channel quality informationfrom the mobile station to the base station BS1 not as transmission asthe CQI in the HSDPA, but as another channel quality information (CQI)signal.

As explained above, when it becomes necessary for the mobile station MSto shift to the peripheral cell detection mode or at the time of thestart of communications between the base station BS1 and the mobilestation MS, by including the frame positions with the possibility oftransmission of packets as parameters of the period A and the offsetvalue in the control information, the mobile station MS can determine aframe position without the possibility of transmission of packets, socan shift to the peripheral cell detection mode at this frame position.By performing this, the mobile station MS can shift to the peripheralcell detection mode, therefore, the mobile station MS and the basestation BS1 do not have to perform processing such as the change of thespread factor SF or the change of the puncturing. Accordingly, theproblem of the transmission and reception processing becoming complex isavoided. Further, frame positions with the possibility of transmissionof packets can be secured, so packets can be reliably transmitted andreceived.

FIGS. 2A and 2B are explanatory views of principal parts of thetransmission and reception functions of the base station, wherein thesetup comprises a transmitting/receiving antenna 1, a circulator 2, atransmitting amplifier 3, an up-converting frequency converter 4, amultiplexer 5, a modulator 6, a controller 7, a pilot channel generator8, channel encoders 9 and 10, a signaling channel generator 11, a packetassembler 12, a scheduler 13, a switch 14, a reference oscillator 15,local oscillators 16 and 17, a low noise amplifier 18, a down-convertingdemodulator 19, a channel separator 20, a mobile station correspondenceprocessing unit 21, a demodulator 22, decoders 23 and 24, a separator25, a pilot demodulator 26, a feedback channel demodulator 27, and adata channel demodulator 28.

In FIG. 2A, the scheduler 13 includes a controlling unit to controltransmission of packets (specifically, to which mobile station) forevery frame based on feedback information from the mobile station (CQIbased on the reception quality (SIR) of the mobile station and theACK/NACK of the acknowledgement of reception), the amount of dataaddressed to each mobile station, and the degree of priority. Further,it is also possible to multiplex the data addressed to a plurality ofmobile stations in the same frame by code division multiplexing,orthogonal frequency division multiplexing, or the like. Further, theswitch 14 selects the data addressed to the mobile station according tothe determination of the scheduler 13. Further, the packet assembler 12assembles the packet from the data addressed to the selected mobilestation, applies processing such as error correction encoding to this bythe channel encoder 10, modulates this in the modulator, and inputs theresult to the multiplexer 5.

Further, the signaling channel generator 11 generates controlinformation (for example modulation type information indicating themodulation scheme for transmitting the data by HS-PDSCH, number of codesof the spreading codes, and pattern information of the rate matchingprocessing applied to the transmission data) corresponding to thepackets addressed to the selected mobile station and applies processingsuch as error correction encoding to this by the channel encoder 9,modulates data via modulator 6, and inputs the result to the multiplexer5. The modulator 6 is provided with configurations of modulatorscorresponding to the pilot channel, the signaling channel, and the datachannel. The multiplexer 5 performs the processing for multiplexing thepilot channel, the signaling channel, and the data channel. Further, thecontroller 7 controls the modulator 6, the multiplexer 5, the localoscillators 16 and 17, the channel separator 20, and the demodulator 22,sets the wireless access scheme, sets the carrier frequency, changes thetransmission frequency or reception frequency by controlling the localoscillators 16 and 17, up-converts the multiplex signal by themultiplexer 5 to the transmission frequency by the frequency converter4, amplifies this by the transmitting amplifier 3, and transmits theresult via the circulator 2 from the antenna 1.

Further, at the reception side of the base station (FIG. 2B), the lownoise amplifier 18 amplifies the signal from the mobile station receivedby the antenna 1, then the frequency converter 19 down-converts this andinputs it to the channel separator 20. This channel separator 20separates the signal from the mobile station to the different channelsby a method in accordance with the wireless access scheme and inputs theresults to the demodulator 22 in the mobile station correspondentprocessing unit 21. FIG. 2B illustrates the case where the result isseparated to a pilot channel, a feedback channel, and a data channel.The demodulator 22 is provided with a pilot demodulator 26, a feedbackchannel demodulator 27, and a data channel demodulator 28 correspondingto the separated channels.

The result of demodulation by the pilot demodulator 26 is used forcompensating for any waveform distortion in the transmission line at thetime of demodulation of the feedback channel and data channel from themobile station. Further, the decoding unit 23 decodes the result ofdemodulation of the feedback channel for decoding the channel encodingand extracting the feedback information from the mobile station andforwards this to the scheduler 13. This feedback information includesthe reception quality information measured at the mobile station (forexample, CQI can be used) and the information of ACK/NACK prepared basedon the data decoding result at the mobile station.

Further, the decoder 24 decodes the result of demodulation of the datachannel for decoding the channel encoding, then the separator 25separates it to the control information and the transmission data andforwards the control information to the scheduler 13. It should be notedthat when a request to shift to the peripheral cell detection mode istransmitted from the mobile station, the request to shift to theperipheral cell detection mode will be included in this controlinformation. Therefore, the scheduler 13 can detect that the measurementof the received signal from a peripheral cell is necessary for themobile station.

Further, even when no request to shift to the peripheral cell detectionmode is transmitted from the mobile station, due to the transmission ofthe channel quality information from the mobile station, the channelquality information will be included in this control information, so thescheduler 13 can detect that the mobile station needs to measure thereceived signal from a peripheral cell. In any case, the scheduler 13further comprises a detecting unit to perform such detection. Further,the scheduler 13 also comprises a control unit, so when detection iscarried out by the detecting unit, the control unit performs schedulingso that wireless frames not containing data for a specific mobilestation among the packets (wireless frames) which are sequentiallytransmitted are discontinuously generated after detection of thedetected specific mobile station. Between these discontinuouslygenerated wireless frames, storage of data for this specific mobilestation is permitted (that is, this specific mobile station is alsotreated as a candidate of transmission at the time of scheduling).

Preferably, between these discontinuously generated wireless frames,desirably the degree of priority is raised for the specific mobilestation so that the possibility of selecting the specific mobile stationfor transmission becomes high. Selection with a high priority enablesthe period during which data is not received becoming longer isprevented. It should be noted that it is not necessary to change theframe length of the wireless frames (wireless sub frames) before andafter such discontinuous generation. Namely, the specific mobile stationcan receive wireless frames having fixed (predetermined) lengths alsoduring the time of cell detection.

The scheduler 13 can function further comprises a notifying unit togenerate instructions to the mobile station for a shift to theperipheral cell detection mode and information of frame positionsallowing (not allowing) packet transmission, and transmitting the same.

It should be noted that the notifying unit can transmit the informationrequired for identifying the discontinuous wireless frames generated bythe above control unit in this way to the specific mobile station. Thesignaling channel can be used as the channel for pre-announcingtransmission to the specific mobile station, and the shared channel isused for transmitting packets (data) to the specific mobile station, andother individual channels. Further, the example of the case where anotification and request between a base station and a mobile station forshifting to the peripheral cell detection mode explained above aremultiplexed on the data channel together with the transmission data fortransmission is shown, but it is also possible to prepare anotherchannel and perform the notification and request between the basestation and the mobile station for shifting to the peripheral celldetection mode on another channel.

FIGS. 3A and 3B are explanatory views of principal parts of thetransmission and reception functions of a mobile station, wherein thesetup comprises an antenna 31, a circulator 32, a transmitting amplifier33, an up-converting frequency converter 34, a multiplexer 35, amodulator 36, a controller 37, a pilot channel generator 38, channelencoders 39 and 40, a feedback channel generator 41, a data channelgenerator 42, a reference oscillator 43, local oscillators 44 and 45, alow noise amplifier 56, a down-converting demodulator 47, a channelseparator 48, a demodulator 49, a received signal quality measuring unit50, decoders 51 and 52, a separator 53, a pilot demodulator 54, asignaling channel demodulator 55, and a data channel demodulator 56.

The transmission side of the mobile station (FIG. 3B) generates thepilot channel by the pilot channel generator 38 and inputs this to themodulator 36. Further, the feedback channel generator 41 generates theinformation to be fed back to the base station (based on the measurementresult (CQI) of the received signal quality measuring unit 50 (FIG. 3A)and the result of decoding in the data channel), applies processing suchas error correction encoding at the channel encoder 39, and inputs theresult to the modulator 36. Further, when there is transmission data andcontrol information (request of shift to the peripheral cell detectionmode, the quality information of the received signal from the basestation from which it receives the service, etc.) to be transmitted tothe base station, the data channel generator 42 performs processing formultiplexing the data, etc., applies processing such as error correctionencoding at the channel encoder 40, and inputs the result to themodulator 36. The modulator 36 is configured to include a modulatorcorresponding to each channel, and inputs a modulated output signalcorresponding to each channel to the multiplexer 35, performs themultiplex processing under the control of the controller 37, up-convertsthe same by the frequency converter 34 to the transmission frequency bywhich the controller 37 controls the local oscillator 44, amplifies itby the transmitting amplifier 33, and transmits the same from theantenna 31 to the base station.

Further, the reception side of the mobile station (FIG. 3A) receives asignal from the base station via the antenna 31, amplifies the receivedsignal by the low noise amplifier 46, down-converts the same by thefrequency converter 47 based on the oscillation output signal of thelocal oscillator 45, and inputs the result to the channel separator 48.The channel separator 48 separates the signal from the base station tothe channels in accordance with the wireless access scheme and inputsthe results to the demodulator 49. The demodulator 49 further comprisesa pilot demodulator 54, a signaling channel demodulator 55, and a datachannel demodulator 56 corresponding to the separated channels, whereinthe demodulator 49 inputs the demodulated output signal of the pilotdemodulator 54 to the signaling channel demodulator 55 and the datachannel demodulator 56, compensates for the distortion of the waveformon the transmission line, inputs the demodulated output signal to thereceived signal quality measuring unit 50, measures the receptionquality of the signal from the base station here, and inputs themeasurement result to the feedback channel generator 41. When a requestto shift to the peripheral cell detection mode and the qualityinformation of the received signal (from the base station from which itreceives the service) are transmitted as the transmission data, themeasurement result of the reception quality is given to a generator (notshown) of transmission data. This transmission data generator (notshown) generates the shift request and quality information based on themeasurement result and outputs the same as the transmission data.

Further, the demodulated output signal of the signaling channel(transmission pre-announcement channel) demodulator 55 is decoded by thedecoder 51. It is decided in each sub frame whether it is a signaladdressed to itself from the base station. When it is a signal addressedto itself (i.e., the specific mobile station), the signaling informationis extracted. This is separated to information for the data channeldemodulation and information for the data channel decoding which areinput to the data channel demodulator 56 and the decoder 52. Further,when this is not a signal addressed to itself (i.e., the specific mobilestation), the processing of the demodulation and decoding of the datachannel is suspended.

Further, when pre-announcement of transmission of the data addressed toitself (i.e., the specific mobile station) is detected by the signalingchannel, the result of the channel encoded demodulation executed by thedata channel demodulator 56 is decoded in the decoder 52 and is furtherinput to the separator 53 and the feedback channel generator 41. Thisseparator 53 separates this input to the control information and thetransmission data and forwards the same to a not shown later circuitportion.

It should be noted that the data channel demodulator 56 and thesignaling channel demodulator 55 acquire information (informationenabling identification of discontinuous frames) notified by thenotifying unit for the base station via either of the data channel orsignaling channel and forwards the information to the controller 37. Asa result, during the period of transmission of discontinuous frames, thecontroller 37 controls the local oscillator 45 to receive the signaltransmitted from the other wireless base station forming the peripheralcells, and makes the received signal quality measuring unit (evaluatingunit) 50 measure the received signal from a peripheral cell.

Then, in the period between discontinuous frames, the mobile stationcontrols the local oscillator 45 to return from the state of receivingthe signal from the other wireless base station forming the peripheralcell to the state of receiving the signal from the base station fromwhich it receives service and receives the signaling. At this time, whenit detects packet are being transmitted addressed to itself (i.e., thespecific mobile station) by the signaling (pre-announcement oftransmission), it controls the data channel demodulator 56 etc. so as toreceive the packets. If no packets are detected, it receives the nextsignaling. Then, when the period between discontinuous frames ends, itcontrols the local oscillator 45 again to receive the signal transmittedfrom another wireless base station forming a peripheral cell andmeasures the received signal from the peripheral cell from the receivedsignal quality measuring unit (evaluating unit) 50. It should be notedthat it is sufficient to measure the received signal from a peripheralcell any time before the completion of measurement is required.

Preferably, after the completion of the measurement, the mobile stationnotifies the completion of the detection of the peripheral cell to thebase station by including a notification of completion in thetransmission data. The scheduler 13 of the base station releases controlover the transmission of the discontinuous frames with respect to thespecific mobile station based on this notification. Further, in the casewhere the notification information and the information of the requestbetween the base station and the mobile station for shifting to theperipheral cell detection mode (including the information of the framepositions with the possibility of transmission of packets explainedabove) are multiplexed on the data channel together with thetransmission data and transmitted, it is also possible to employ aconfiguration preparing another channel and performing the notificationand request between the base station and the mobile station for shiftingto the peripheral cell detection mode. Further, the mobile station mayalso be provided with a controller for transmitting a request to shiftto the peripheral cell detection mode to the base station when theresult of measurement of the reception quality by the received signalquality measuring unit 50 is also input to the controller 37 where it iscompared against a threshold value to detect if the reception qualityfalls to less than the threshold value.

Second Embodiment

FIGS. 4A and 4B are explanatory views of a second embodiment of thepresent invention, in which FIG. 4A is a schematic view of a wirelesscommunications system. The base stations BS1 and BS2 are systems fortransmission and reception in a wireless communications system where thewireless access schemes can be, for example, W-CDMA or OFDM-basedschemes. The base station BS1 uses a wireless scheme 1, while the basestation BS2 uses a wireless scheme 2. When a mobile station MS engagesin wireless communications with the base station BS1 and moves in thedirection of the base station BS2 while receiving the data packets, thereception quality from the base station BS1 is gradually lowered.Therefore, the processing for detection of a peripheral cell becomesnecessary for handover.

In this case, the base station BS2 of the peripheral cells is configuredto transmit by the wireless scheme 2, therefore the mobile station MScannot simultaneously handle the wireless schemes 1 and 2. Therefore, inthe same way as the above explained case, the mobile station MS performsprocessing for shifting to the peripheral cell detection mode. Namely,the mobile station determines the frame positions with the possibilityof transmission of data packets and the frame positions without thepossibility with the base station BS1 via the control channel etc. andswitches to the peripheral cell detection mode at a frame positionwithout the possibility of transmission of packets. In this case, themobile station switches from the wireless scheme 1 to the wirelessscheme 2 and receives and judges the transmission signal by the commonchannel of the base station BS2. In this case, in place of switching thefrequency of the local oscillators 16, 17, 44, and 45 in FIGS. 2A, 2Band FIGS. 3A, 3B, switching of the demodulator and modulator isprovided.

In FIG. 4B, the frames with the possibility of transmission of packetsare shown by hatching, while the frames without the possibility oftransmission of packets are shown otherwise. Without shifting to thecompressed mode, the mobile station MS shifts to the peripheral celldetection mode at a frame position without the possibility oftransmission of packets determined with the base station BS1. In thisperipheral cell detection mode, as previously explained, it switchesfrom the wireless scheme 1 to the wireless scheme 2 to measure thereception quality from the base station BS2. When the reception qualityfrom the base station BS1 by the wireless scheme 1 falls to less than,for example, the reception quality by the wireless scheme 2 from thebase station BS2, the mobile station MS transmits a request for handoverprocessing, switches from the base station BS1 to the base station BS2by known various controlling means, and continues the reception of thepackets.

For example, in the same way as the case of the frequencies f1 and f2,by limiting the numbers of the frames with the possibility oftransmission of packets to frames designated by the period A and theoffset value B like for example A×n+B (where n is an integer), themobile station uses the period of frames without the possibility oftransmission of packets (A−1) to switch from the wireless scheme 1 tothe wireless scheme 2 and shifts to the detection mode of a peripheralcell of a different scheme. The period A and the offset value B in thiscase can be made variable in accordance with the type of the data forcommunication in the visiting cell (differing in the permitted delaytime and the bit rate to be compensated), the user ID, the ability ofthe user, etc. Further, it is also possible to transmit packets byconsecutive frames. Further, the numbers of the frames allowingtransmission of packets of the heads of consecutive packets can bedetermined like A×n+B (where n is an integer) explained above. It shouldbe noted that it is also possible to employ a wireless communicationssystem wherein the same base station uses a plurality of wirelessschemes and assign a wireless scheme selected from among the pluralityof wireless schemes to the mobile station corresponding to the state ofcongestion of the communication of this base station or by detecting thedeterioration of the reception quality. Further, it is within the scopeof the present invention to instruct the switching of the wirelessschemes and the switching of frequencies to the mobile station in awireless communications system, wherein the same base station can switchamong a plurality of frequencies and switch among a plurality ofwireless schemes.

Third Embodiment

FIGS. 5A and 5B are explanatory views of a third embodiment and a fourthembodiment of the present invention. The third embodiment of the presentinvention shown in FIG. 5A shows a case of using the procedures of thefollowing (1) to (6) when shifting to the peripheral cell detectionmode. That is,

(1) when the base station or the mobile station detects the conditionsfor shift to the peripheral cell detection mode due to the drop of thereception quality etc. in the normal mode,

(2) information of (1) is notified/communicated between the base stationand the mobile station, and information concerning the frames with thepossibility of transmission of packets in the peripheral cell detectionmode (parameters such as the period A and offset value B and duration)are notified from each other;

(3) the above (2) is acknowledged;

(4) the mobile station shifts to the peripheral cell detection mode byconfirming the acknowledgement,

(5) the mobile station monitors for signaling of the original basestation and receives any packets addressed to itself in frames with thepossibility of transmission of packets, detects and measures aperipheral cell by the peripheral cell detection mode in frames withoutthe possibility of transmission of packets; and

(6) after the end of a period enabling a shift to the peripheral celldetection mode, that is, the end of a frame period without thepossibility of transmission of packets, the normal mode is returned to.

In the procedures of the above (2) and (3), it is within the scope ofthe present invention to notify the information (parameters such asperiod and duration) concerning frames with the possibility oftransmission of packets in the peripheral cell detection mode by asingle signal. Even when a relatively long time is taken for detecting aperipheral cell, the drop in the transmission efficiency due to thesignaling along with the shift to the peripheral cell detection mode canbe limited to the lowest level. Further, the time of the frames able tobe used for the packet transmission can be secured, therefore theperipheral cell can be detected while maintaining the speed of the datacommunications with the original base station to a certain extent.Further, the above procedures can be realized by the controlling unit ofthe controller 37 of the mobile station shown in FIG. 3A.

Fourth Embodiment

In fourth embodiment of the present invention shown in FIG. 5B, fordesignating the frames with the possibility of transmission of packetsin the peripheral cell detection mode, the period A and the offset valueB are designated as the parameters of the peripheral cell detection modebetween the base station and the mobile station. The offset value B isan amount indicating from which frame the frames with the possibility oftransmission of packets first begin from a certain time reference (forexample, the frame of the system frame number (SFN)=0). Further, theperiod A is the period between one frame and another frame with thepossibility of transmission of packets and shows a case where a framewith the possibility of transmission of packets is designatedperiodically, one time every A number of frames. Accordingly, in thesections of the remaining (A−1) number of frames, it is possible toshift to the peripheral cell detection mode.

Fifth Embodiment

FIG. 6 is an explanatory view of a fifth embodiment of the presentinvention and shows a case where the detection of a peripheral cell isenabled by the procedures of (1) to (12). In the above fourthembodiment, the frames with the possibility of transmission of packetswere limited to only the frames designated in a certain period, but thefifth embodiment employs a system configuration allowing continuouspacket transmission in consecutive frames in addition to periodic framesso as to enable a case where the traffic increases during the peripheralcell detection mode. For this reason, the base station and the mobilestation designate between them the period A and the offset value B asthe parameters of the peripheral cell detection mode and designate theframes allowing the start of packet transmission (the hatched frames(1), (4), and (9)) using the period A and the offset value B. When thereis packet transmission in these frames, the packets may be transmittedin the same way in the following frames (2), (5), and (10). Therefore,the existence of any packet transmission is monitored.

In the illustrated case, as the result of monitoring for reception ofpackets in the frame (2), no packet transmission is detected. Therefore,in the next frame (3) on, it is decided there is no packet transmissionat the frame positions and the peripheral cell detection mode can beshifted to. Further, packet transmission is detected at the frame (5)and the next frame (6), so the existence of the packet transmission inthe next frame (7) is monitored. When it is detected that no packettransmission is then carried out, the peripheral cell detection mode canbe shifted to in the frame (8) next to the frame (7), and so on. In thesame way, when there is no packet transmission in the frame (11) next tothe frame (10), the peripheral cell detection mode can be shifted to inthe next frame (12), and so on. Accordingly, even when the trafficincreases in the peripheral cell detection mode and the packets to betransmitted increase, packet transmission in consecutive frames can beenabled. Therefore, the rate of the data communications with the basestation connected with at present can be raised without returning to thenormal mode, etc. The controlling unit, in this case, can be realizedby, for example, the processing functions of the scheduler 13 shown inFIG. 2A and the controller 37 shown in FIG. 3A.

Sixth Embodiment

FIGS. 7A and 7B are explanatory views of a sixth embodiment of thepresent invention, in which FIG. 7A shows an example of a case where thetransmission rate is high, and FIG. 7B shows an example of a case wherethe transmission rate is low. This shows an embodiment where the numberof frames with the possibility of transmission of packets in theperipheral cell detection mode is made variable depending on the type ofthe wireless communications (nature of transmission rate, etc.) with thebase station to which the mobile station is presently connected. Whenthe characteristic of the data communications (for example, the datatransmission rate) with the presently connected base station is large,or when the guaranteed bit rate is large or when the permitted delaytime is small, as shown in FIG. 7A, the period A1 of the frames with thepossibility of transmission of packets is set short. Conversely, whenthe transmission rate is small or the guaranteed bit rate is small andthe permitted delay time is long, as shown in FIG. 7B, the period A2 ofthe frames with the possibility of transmission of packets is set long.It should be noted that, the case where the offset value B is madeconstant is shown, but this offset value B can also be made variable.

Seventh Embodiment

FIGS. 8A and 8B are explanatory views of a seventh embodiment and aneighth embodiment of the present invention. In the seventh embodiment ofthe present invention shown in FIG. 8A, the period A1 of the frames withthe possibility of transmission of packets and the offset value B1 areset with respect to the user 1, and the period A2 of the frames with thepossibility of transmission of packets and the offset value B2 are setwith respect to the other user 2. In this case, it is possible to makethe offset values B1 and B2 the same and make the periods A1 and A2different or conversely make the periods A1 and A2 the same and make theoffset values B1 and B2 different. Further, by making at least one ofthe period or offset value different as explained above for a pluralityof users, concentration of the packet transmission for a large number ofusers at the same time can be avoided.

Eighth Embodiment

In the eighth embodiment of the present invention shown in FIG. 8B, theperiod of the frames with the possibility of transmission of packets ofthe packet and offset value are set to become different for each of thebase stations 1 and 2. That is, the case where the offset value B1 forthe base station 1 and the offset value B2 for the base station 2 aremade different and where the period A1 of the frames for the basestation 1 and the period A2 of the frames for the base station B2 aremade different is shown. Due to this, even when the common channel fromthe base station used for detecting a peripheral cell is not alwaystransmitted, the detection of a peripheral cell can be enabled. Forexample, this is a communication format where the pilot is transmittedonly when data packets are transmitted. Here, in the case of using thepilot channel attached to a packet addressed to another mobile stationfor detecting a peripheral cell and when one mobile station is connectedto each base station at adjacent base stations and the mobile stationsconnected to each base station detect peripheral cells at almost thesame time, at least one of the period or offset value is made differentfor each adjacent base station. By transmitting the packets at timingsdifferent from each other in this way, it becomes possible to detect aperipheral cell by using the pilot channel accompanied with a packetaddressed to the mobile station connected to the base station formeasurement.

Ninth Embodiment

In ninth embodiment of the present invention shown in FIG. 8B, a packetcommunications system like the HSDPA explained above performs AMC(Adaptive Modulation and Coding) for adaptively changing the encodingunit (encoding rate, etc.) of the error correction encoding scheme andthe modulation scheme in accordance with the environment of thetransmission line between the base station and the mobile station. Bymeasuring the SIR from for example the received signal quality measuringunit 50 shown in FIG. 3A etc. in the mobile station, the mobile stationgenerates the reception quality information of the transmission line(CQI=Channel Quality Information) and reports this to the base stationby the feedback channel. In the mobile station in that case, when it isdetected that the measured SIR or reported CQI value becomes lower thana certain set value, that is, when it is detected in, for example, thecontroller 37 in FIG. 3A that the measured SIR or reported CQI valuebecomes lower than the threshold value, a peripheral cell detection modeshift request is transmitted from the mobile station to the basestation. At a frame position other than a frame position with thepossibility of transmission of packets explained above, a shift is madeto the peripheral cell detection mode. In this case, the frame positionswith the possibility of transmission of packets in adjacent cells orsectors can be set different from each other. Further, it is alsopossible to change the period of the frame positions with thepossibility of transmission of packets and offset value all the time.

10Th Embodiment

A 10th embodiment of the present invention, in the same way as the caseof the ninth embodiment explained above, provides a packetcommunications system like HSDPA which performs AMC (Adaptive Modulationand Coding) for adaptively changing the encoding unit (encoding rate,etc.) of the error correction encoding scheme and the modulation schemein accordance with the environment of the transmission line between thebase station and a mobile station. The mobile station measures the SIRby, for example, the received signal quality measuring unit 50 shown inFIG. 3A, generates the reception quality information of the transmissionline (CQI=Channel Quality Information), and reports this information tothe base station. Therefore, when the base station detects by, forexample, the scheduler 13 etc. shown in FIG. 2A that the CQI valuereported from the mobile station has become lower than a certain setvalue, the base station can request the mobile station to shift to theperipheral cell detection mode.

While the invention has been described with reference to specificembodiments chosen for purpose of illustration, it should be apparentthat numerous modifications could be made thereto by those skilled inthe art without departing from the basic concept and scope of theinvention.

What is claimed is:
 1. A wireless base station which transmits data to amobile station, said wireless base station comprising: a modulatorconfigured to modulate notification of frame information and transmitthe notification to a certain mobile station if the certain mobilestation requires a measurement of radio signals of a different frequencyor of a different system via a shared channel, the frame informationenabling identification of wireless frames that do not have apossibility of transmission of packets from the wireless base station tothe certain mobile station and at which the certain mobile station isallowed to measure radio signals transmitted from another wireless basestation, without receiving data via the shared channel by which data istransmitted to any selected mobile station from said wireless basestation, which wireless frames allowing the measurement of the radiosignals are variable in a repetition period and an offset valueindicated by the frame information; and a scheduler configured toprohibit data transmission to said certain mobile station via saidshared channel during said frame indicated by said frame information. 2.The wireless base station according to claim 1, wherein said frameinformation indicates frames in which said certain mobile station isallowed to measure radio signals transmitted from said another wirelessbase station without receiving data from said wireless base station. 3.The wireless base station according to claim 2, wherein time periods formeasuring defined by said frame information are separated from eachother.
 4. The wireless base station according to claim 3, wherein aninterval of starting timings of said measuring time periods correspondsto a certain period.
 5. The wireless base station according to claim 4,wherein the frame information indicates said certain period.
 6. A methodfor data transmission from a wireless base station to a mobile station,said method comprising: modulating notification of frame information andtransmitting the notification to a certain mobile station if the certainmobile station requires a measurement of radio signals of a differentfrequency or of a different system via a shared channel, the frameinformation enabling identification of wireless frames that do not havea possibility of transmission of packets from the wireless base stationto the certain mobile station and at which the certain mobile station isallowed to measure radio signals transmitted from another wireless basestation, without receiving data via the shared channel by which data istransmitted to any selected mobile station from said wireless basestation, which wireless frames allowing the measurement of the radiosignals are variable in a repetition period and an offset valueindicated by the frame information; and prohibiting data transmission tosaid certain mobile station via said shared channel during said frameindicated by said frame information.
 7. The method according to claim 6,wherein said frame information indicates frames in which said certainmobile station is allowed to measure radio signals transmitted from saidanother wireless base station without receiving data from said wirelessbase station.
 8. The method according to claim 7, wherein time periodsfor measuring defined by said frame information are separated from eachother.
 9. A mobile station which receives data transmitted in a framefrom a wireless base station, said mobile station comprising: an antennaconfigured to receive radio signals transmitted from the wireless basestation; a demodulator configured to demodulate radio signals receivedby said antenna and obtain notification of frame information from thewireless base station if the mobile station requires a measurement ofradio signals of a different frequency or of a different system via ashared channel, the frame information enabling identification ofwireless frames that do not have a possibility of transmission ofpackets from the wireless base station to the mobile station and atwhich said mobile station is allowed to measure radio signalstransmitted from another wireless base station, without receivingcertain data via the shared channel by which data is transmitted to anyselected mobile station from said wireless base station, which wirelessframes allowing the measurement of the radio signals are variable in arepetition period and an offset value indicated by the frameinformation; and a measurement unit configured to perform measurement ofradio signals transmitted from said another wireless base station byusing said frames indicated by said frame information.
 10. The mobilestation according to claim 9, wherein time periods for measuring definedby said frame information are separated from each other.
 11. The mobilestation according to claim 10, wherein starting timings of saidmeasuring time periods have a certain interval.
 12. The mobile stationaccording to claim 11, wherein the frame information indicates saidcertain interval.
 13. A method for data reception used by a mobilestation which receives data transmitted in a frame from a wireless basestation, said method comprising: receiving radio signals transmittedfrom the wireless base station by an antenna; demodulating radio signalsreceived by said antenna to obtain notification of frame informationfrom the wireless base station if the mobile station requires ameasurement of radio signals of a different frequency or a differentsystem via a shared channel, the frame information enablingidentification of wireless frames that do not have a possibility oftransmission of packets from the wireless base station to the mobilestation and at which said mobile station is allowed to measure radiosignals transmitted from another wireless base station, withoutreceiving certain data via the shared channel by which data istransmitted to any selected mobile station from said wireless basestation, which wireless frames allowing the measurement of the radiosignal are variable in a repetition period and an offset value indicatedby the frame information; and performing measurement of radio signalstransmitted from said another wireless base station by using said framesindicated by said frame information.
 14. The method according to claim13, wherein said notification is transmitted to said mobile station togenerate said frames after radio communication, via said shared channel,between said wireless base station and said mobile station is started.